Text. The Heart and the Vascular Sy

Text. The Heart and the Vascular System
The heart is an inner hollow muscular organ placed within the chest and included in the
pericardium. The base of the heart is against the third rib. Its apex is against the interspace
between the fifth and sixth costal cartilages. The weight of the heart is about 300 grams (gr) in
the male and about 220 gr in the female.
The heart consists of two separate chambers divided by the septum. Each of the chambers has
two connected parts: the atrium and the ventricle.
The right atrium is larger than the left one, but the walls of the left atrium are thicker than those of the right one. The left ventricle is the largest and strongest in the heart. The right ventricle is triangular (треугольный) in form and has thick walls. The
right ventricle is in the anterior part of the heart. The left ventricle is longer and more conical than the right one. The walls of the left ventricle are three times as thick as the walls of the right one. As it is required to pump blood to the rest of the body it needs to have more muscle than the other chambers. The heart muscle itself is called the myocardium.
Coordination of blood flow through the heart is maintained by electrical activity and four heart valves. These valves open and close to allow blood to flow in thecorrect direction only. The valves are located at the entrance and exit of each ventricle. The atrioventricular valves separate the atria from the ventricles. The four heart valves are:
*The tricuspid valve which controls blood flow between the right atrium and right ventricle.
* The pulmonary valve which lies between the right ventricle and pulmonary artery. The pulmonary artery takes deoxygenated blood from the heart to the lungs.
* The mitral valve which allows oxygen-rich blood from the lungs to flow between the left atrium and left ventricle.
* The aortic valve which controls blood flow between the left ventricle and the main blood vessel leaving the heart called the aorta.
The rhythmic contraction of the heart is governed by an electrical impulce.
The muscular structure of the heart consists of fibrous bands divided into two groups — the
first ones are the fibrous bands of the atria and the second ones are the fibrous bands of the
ventricles.
The vascular system consists of three groups of vessels — arteries, veins and capillaries.
The vessels carrying blood to and from the tissues of the body compose the general system.
They are called the systemic vessels.
The pulmonary system is formed by the vessels carrying blood to and from the lungs.
The portal system is formed by the veins passing to the liver.
Most of the arteries are composed of three coats. The arteries dilate and contract
simultaneously with the action of the heart.